(1) Field of the Invention
The present invention relates to an improved antenna system for enhancing the communication capabilities of individuals or vessels operating within high latitude regions covered with sea ice.
(2) Description of the Prior Art
Radio communication systems are old and well known in the art. These systems typically include a device for transmitting a radio frequency signal and for receiving a transmitted signal. Often, the environment in which the transmitter/receiver device and an associated antenna is located affects the ability to transmit or receive signals at particular frequencies. For example, in the Arctic, the reliability of high frequency signals, i.e., signals in the range of 2-30 MHz, is greatly diminished as a result of the high degree of solar activity concentrated within that region. This makes communications greater than 50 miles either difficult or impossible for extended periods.
Recognizing the environmental impact on the ability to receive or transmit signals, antenna systems have been developed that utilize the surrounding environment to enhance the communication system. U.S. Pat. No. 1,349,103 to Rogers illustrates one such system. Rogers discovered that grounded antennas are highly efficient when disposed horizontally or substantially parallel to the surface of the Earth, and surrounded by or enclosed in a uniform metallic screen but insulated therefrom. In one embodiment of his invention, Rogers illustrates two antennae extending substantially parallel to the Earth's surface in different directions from the signal instruments. Each of the antennae are enclosed in a metal screen or pipe. At its outer end, each antenna is connected to earth plates buried in the ground. Rogers states that the antennae may be positioned either above ground or below ground.
Rogers also notes that his invention is equally applicable to boats or vessels such as submarines. In FIG. 5 of the Rogers' patent, a shipboard antenna system is illustrated. In this system, the antennae are located in tubes or pipes mounted within the hull of the vessel. Each antenna is connected to a ground plate externally mounted to the vessel.
U.S. Pat. No. 4,839,661 to Losee illustrates yet another type of communication system which includes one or more substantially linear, electrically insulated radiating elements buried in the ground. The effective electrical length of each radiating element is equal to at least one-third of the wavelength of the electromagnetic signals being propagated. The efficiency of the system is increased, particularly when operating at high frequencies, by surrounding the radiating element(s) with a low loss dielectric substance such as crushed rock. The gain of the system is increased by forming an underground array comprising a plurality of radiating elements positioned substantially parallel to one another.
Neither of these patents however addresses the problems of communication systems in Arctic-type environments.
The present invention takes advantage of the discovery that sea ice provides a means for guiding radio waves at low attenuation in the 500 KHz frequency range. This low attenuation, along with the very low radio noise present in this region, makes this communication mode quite useful. The use of the 500 KHz maritime mobile frequency band for vessels at sea has been limited to large vessels or structures capable of supporting the large several hundred to one thousand foot wire lengths necessary for efficient utilization of this band. No antenna system has been available for this band for portable or emergency use specifically utilizing the waveguide properties of sea ice.
Accordingly, it is an object of the present invention to provide an antenna system which utilizes the waveguide properties of sea ice to transmit signals in the 500 KHz frequency range. It is a further object of the present invention to provide an antenna system that can be used in emergencies.
It is yet a further object of the present invention to provide an antenna system which is portable and does not require the use of long wire lengths or tail structures.
Still other objects and advantages of the present invention will become more apparent from the following description and drawings wherein like reference numerals depict like elements.